The treatment and cure of autoimmunity remains of paramount importance. The challenges to developing successful therapies are broad, ranging from complex genetics, similarities and differences among target tissues, differential pathogenic mechanisms and an incomplete knowledge of the target antigens. We have shown that the Non-Obese Diabetes (NOD) mouse strain can be used as a mouse model of multiple autoimmune disorders (AID). These other autoimmune diseases were most apparent when regulatory T cells (Tregs) were eliminated and co-stimulatory pathways altered. For instance, NOD mice develop a spontaneous autoimmune disease of the peripheral nervous system, termed Spontaneous Autoimmune Peripheral Polyneuropathy (SAPP), in the absence of CD28 interaction with B7-2. In addition, we observed that in the complete absence of CD28 signals, NOD mice were deficient in Tregs and developed SAPP, sialadenitis, autoimmune thyroiditis and a newly appreciated autoimmune exocrine disease similar to that observed in "fulminant type 1 diabetes" described in Japanese and some Australian patients. Significantly, these various autoimmune diseases could use different pathogenic and co-stimulatory pathways and result from the recognition of distinct as well as potentially overlapping self-antigen specificities. These results have led to the conclusion that the NOD mouse represents a unique model for studying multi-organ autoimmunity. The combination of genetic propensity for autoimmunity and the tools that we have developed in this mouse strain will be exploited to address several key questions. Do unique and/or overlapping antigen specificities distinguish/link these diseases? Are the pathogenic pathways evident for one disease critical for the manifestation of others? Are there common co-stimulation pathways that control the susceptibility and progression of these distinct autoimmune diseases? The following aims are proposed to address these questions: Specific Aim #1: To generate tissue antigen-specific effector and regulatory T cell TCR Tg mice based on candidate antigens. Specific Aim #2: To generate tissue antigen-specific effector and regulatory T cell TCR Tg mice using T cell hybridomas and mimotopes. Specific Aim #3: To determine the effector and regulatory pathways and the role of co-stimulation in the distinct autoimmune diseases in NOD mice. Specific Aim #4: To develop green fluorescence protein (GFP)-specific systems to study autoimmunity in NOD mice. Together, the results of these studies will test the hypothesis that the phenotypic manifestation of multi- organ autoimmune diseases is regulated by a coalescence of common and tissue-specific pathways. Moreover these common and distinct pathways are critical for understanding of the immunopathology of these different autoimmune diseases and development of novel therapies.